The present invention relates to bypassing a door interlock mechanism on an enclosure housing electrical apparatus, and, more particularly, to bypassing a door interlock mechanism on an enclosure housing electrical apparatus while the apparatus is energized.
Enclosures housing electrical apparatus of significant voltage typically include a mechanical interlock device to prevent entry into the enclosure without first removing power to the circuit. This mechanical interlock device may, however, need to be bypassed or defeated to allow access to the components of the apparatus while the circuit is still energized. For example, it may become necessary to access the electrical apparatus while the components are still live to check thermal connections and current connections within the circuit.
One particular method of defeating a locking mechanism on an enclosure housing electrical apparatus when a circuit is energized is described in U.S. Pat. No. 5,963,420 entitled xe2x80x9cInterlock Bypassxe2x80x9d. In that patent, when the breaker switch is in an xe2x80x9conxe2x80x9d position, the door is locked closed by a slidable plate having an aperture therein located in the surface of the door adjacent the breaker switch. In the locked mode, the sliding plate is positioned such that the aperture in the door is prevented from opening over the breaker switch. The locking mechanism is defeated by inserting a key into a receptacle and turning the key to slide the plate so that the aperture is positioned over the breaker switch. When the aperture is properly positioned, the breaker switch is no longer obstructed by the plate, and the door is allowed to swing open over the breaker switch.
In an exemplary embodiment of the invention, a defeatable interlock mechanism for an electrical equipment enclosure requiring a circuit breaker to be tripped before opening is described. The defeatable interlock mechanism includes a support platform having an operator handle stem operably connected to the circuit breaker, an interlock slide plate positioned in a parallel planar relationship with the support platform and having a slot for receiving a door interlock pin therein, and a lever operably connected to the interlock slide plate and configured to defeat the interlock mechanism when the door interlock pin is engaged with the slot, thereby allowing the door to be opened while the circuit is energized.
The lever of the inventive mechanism is an elongated member pivotally supported at a fulcrum point intermediate the first and second ends of the lever. The first end of the lever is accessible from an exterior of the electrical equipment enclosure, and the second end of the lever is pivotally connected to the interlock slide.
An escutcheon is situated on the front of the electrical equipment enclosure door through which the first end of the lever projects. The lever is fixedly secured within the escutcheon by a retaining member that holds the lever steadfast. The retaining member is typically a lockout screw positioned transverse to the general movement of the lever. Removal of the retaining member requires the use of a tool such as a screwdriver or Allen head wrench.
Electrical systems may require an operator to access the internal components of the circuit while the system is energized. Utilizing the interlock defeating device of the present invention enables the door of an electrical equipment enclosure to be opened while the circuit is not tripped, thereby giving the operator access to the components of the circuit for maintenance procedures or system testing. Removal of the retaining member using a tool forces the operator to make a conscious and voluntary effort to gain access to the enclosure and prevents the operator from inadvertently gaining access and encountering a hazardous condition.